Royal Institution. 223 



universal law of magnetic action. Ordinary magnetic action may- 

 be divided into two kinds ; that between magnets permanently 

 magnetized and unchangeable in their condition, and that between 

 bodies of which one is a permanent unchangeable magnet, and the 

 other, having no magnetic state of its own, receives and retains its 

 state only whilst in subjection to the first. The former kind of action 

 appears in the most rigid and pure cases to be subject to that law; 

 but it would be premature to assume beforehand, and without abun- 

 dant sufficient evidence, that the same law applies in the second set 

 of cases also ; for a hasty assumption might be in opposition to the 

 truth of nature, and therefore injurious to the progress of science, by 

 the creation of a preconceived conclusion. We know not whether 

 such bodies as oxygen, copper, water, bismuth, &c., owe their re- 

 spective paramagnetic and diamagnetic relation to a greater or less 

 facility of conduction in regard to the lines of magnetic force, or to 

 something like a polarity of their particles or masses, or to some as 

 yet unsuspected state ; and there is little hope of our developing the 

 true condition, and therefore the cause of magnetic action, if we 

 assume beforehand the unproved law of action and reject the expe- 

 riments that already bear upon it ; — for Pliicker has distinctly stated 

 as the fact, that diamagnetic force increases more rapidly than mag- 

 netic force, when the power of the dominant magnet is increased ; 

 and such a fact is contrary to the law above enunciated. The fol- 

 lowing are further results in relation to this point. 



When a body is submitted to the great unchanging Logeman 

 magnet in air and in water, and the results are reduced to the Centi- 

 grade scale, the relation of the three substances remain the same 

 for the same distance, but not for different distances. Thus when 

 a given cylinder of flint-glass was submitted to the magnet sur- 

 rounded by air and by water, at the distance of 0'3 of an inch, as 

 already described, it proved to be diamagnetic in relation to both ; 

 and when the results were corrected to the Centigrade scale, and 

 water made zero, it was 9°"1 below, or on the diamagnetic side of 

 water. At the distance 0"4 of an inch it was 10°'6 below water; 

 at the distance of 0*7 it was 12°'l below water. When a more dia- 

 magnetic body, as heavy glass, was employed, the same result in a 

 higher degree was obtained ; for at the distance of 0*3 it was 37°*8 

 below water, and at that of 0-8 it was 48°* 6 beneath it. Bismuth 

 presented a still more striking case, though, as the volume of the 

 substance was necessarily small, equal confidence cannot be placed 

 in the exactitude of the numbers. The results are given below for 

 the three substances, air being always 100° and water 0° ; the first 

 column of figures for each substance contains the distance * in tenths 



* A given change of distance necessarily implies change in degree of 

 force, and change in the forms of the lines of force ; but it does not imply 

 always the same amount of change. The forces are not the same at the 

 same distance of 04 of an inch in opposite directions from the axial line 

 towards m and n in the figure, p. 219, nor at any other equal moderate 

 distance ; and though by increase and diminution of distance the change is 

 in the same direction, it is not in the same proportion. By fitly arranged 

 terminations, it may be made to alter with extreme rapidity in one direc- 

 tion, and with extreme slowness or not at all in another. 



